In motor vehicles in particular, even today a large number of functions are triggered or controlled via remote controls. Usually a radio link in the license-free frequency bands is used for transmission from and to the motor vehicle. To gain access to the motor vehicle and also to start the engine for example what are known as “Remote Keyless Entry” systems (abbreviated to RKE systems) for wireless central locking are used. RKE systems have now become the standard solution not only for convenient locking and unlocking of a motor vehicle but also for other convenience functions. They operate by means of a radio control generally integrated into the vehicle key, which is additionally used, as well as for locking and unlocking the doors and the trunk, for activating or deactivating the burglar alarm and the immobilizer accordingly. Other functions such as convenient opening and closing of windows, sun roofs, sliding doors or hatchbacks can also be integrated into the system. A further convenience function and safety function is the activation of the front lighting of the motor vehicle. Additional safety is provided by a so-called emergency button integrated into the key which, when pressed, triggers an audible and visual alarm on the motor vehicle. Publication DE 102 33 597 A1 describes the functioning of such an RKE system and a method for warning about illegal attempts to access the vehicle.
Such RKE systems operate in such cases as required with unidirectional or bidirectional communication within the range of internationally enabled ISM frequencies. Further typical features are secure data transmission with optionally increased security by way of a challenge-response authentication method (bidirectional) and also low energy consumption. In addition further applications allow the functions of an RKE system to be personalized to selected persons. The operating range of such RKE systems is usually up to 100 m.
A further system based on radio communication is the so-called PASE system. PASE stands for PAsive Start and Entry and describes a keyless entry and start system. With this keyless vehicle entry system the driver only has to carry an identification transmitter (ID) with them and is given access to the vehicle simply by touching the door handle. As soon as the driver is inside the vehicle, the engine can be started by pressing a button. If the driver leaves the vehicle, the PASE system locks the vehicle either automatically or at the touch of a button. The drivers identification device replaces conventional mechanical or radio-controlled keys and is designed to give the driver maximum convenience and be very easy to use. Here too there is the option of personalization to selected persons and multi-channel bidirectional data transmission is usually used which is also undertaken wirelessly and encrypted, for example in the range of internationally enabled ISM frequencies.
There are also currently systems with other functions establishing themselves in the field of motor vehicles, such as the transmission of status information for example. Such systems generally operate over greater distances, usually several hundred meters. Examples of such systems are what is known as Telestart, i.e. starting an engine from long distances, or remote control of a static heater, an automatic climate control system and so forth. Further examples for the use of radio links with large ranges other than those of the RKE and PASE systems described relate to status information about the motor vehicle able to be called up from longer distances, such as the current status of its locks, the current internal temperature and the results of technical system checks (technology check). The transmission of alarm messages is also desirable over a longer distance.
All functions requiring wireless data transmission over longer distances are also grouped together under the generic term “long-range applications”. An objective for long-range applications is to provide data transmission or communication respectively over distances of at least 600 m. Arrangements already available for long-range applications have thus for been predominantly “isolated” arrangements, which for various reasons have a separate control unit with corresponding identification (ID) and a separate controller in the motor vehicle.
To improve the operating convenience for the user there is great interest in implementing radio communication for RKE, PASE and long-range applications in just one single system. For the user this means that he would only use and need to carry with him one peripheral unit (e.g. mobile control unit, remote control) with which he can control all desired functions. At the same time it is useful as regards costs for only a single controller to have to be built in on the vehicle side which controls all the said functions.
It is also desirable for the vehicle-side controller to also be embodied for checking and testing the tire pressure, with the peripheral unit then being a tire pressure sensor. Arrangements for checking the tire pressure and typically known by names such as “Tire Guard” or TPMS (Tire Pressure Monitoring System). Tire Guard is a so-called direct tire pressure checking system in which battery-powered sensors attached to the wheels continuously measure the tire pressure. The coded information about the current tire pressure in this case is transmitted as a high frequency signal to the receiver and the corresponding data is evaluated by special software in a control unit and displayed on the dashboard. In such cases the sensors attached to the wheels of the motor vehicle likewise operate in license-free frequency bands (usually at 315 MHz and 433.92 MHz) and thus also in the frequency ranges used by RKE and PASE.
An integration of standard arrangements such as for example RKE, PASE, Tire Guard or TPMS arrangements, as well as the long-range applications into one system is desirable for various reasons. From the user's viewpoint this means for example that he only need carry with him one peripheral unit typically equipped as a mobile operating device, with which he can control all the said functions. On the other hand it is desirable in relation to costs for example to provide just a single controller which performs the vehicle-side wireless communication and control sequences for the said functions.
However in such cases different, sometimes conflicting demands made on the vehicle-side controller have to be fulfilled. These differing demands typically relate to the frequency band used in each case, the modulation method, the data transmission rate, the necessary bandwidth, the sensitivity of the receiver unit, the required transmit power and the respective antenna characteristics for transmitting and receiving the relevant signals.